This application claims the benefit of Japanese Patent Application Number 2013-099581 filed on May 9, 2013, and Japanese Patent Application Number 2014-015821 filed on Jan. 30, 2014, the entirety of which is incorporated by reference.
Field of the Invention
The present invention relates to reciprocating cutting tools that cut a workpiece by reciprocating a blade, such as jigsaws.
Description of Related Art
As shown in Japanese Patent Application Publication No. 2001-347502 (JP 2001-347502 A), a reciprocating saw is known which includes a detachable saw blade (blade), a plunger (rod) capable of linearly reciprocating along a vertical reference line, and a balance weight capable of linearly reciprocating above the plunger along the reference line.
Each of the plunger and the balance weight has a guide member protruding rearward. A gear is disposed so as to receive these guide members with a common elliptic guide groove. As the gear rotates, each guide member is guided by the guide groove. The plunger and the balance weight are located closest to each other when the guide members are located at intersections with the minor axis of the guide groove. The plunger and the balance weight are located farthest from each other when the guide members are located at intersections with the major axis of the guide groove. The plunger and the balance weight thus reciprocate at symmetrical positions.
As shown in Japanese Patent Application Publication No. 2011-115912 (JP 2011-115912 A), a reciprocating tool is known which rotates a gear having, in its front part, a gear eccentric portion and a needle controller located on the opposite side to the gear eccentric portion, and which vertically reciprocates a plunger via a sleeve receiving the needle roller and a connector, and vertically reciprocates a balance weight via an elliptic hole receiving the gear eccentric portion.
The gear eccentric portion is shorter in a longitudinal direction than the needle roller of the gear, and the balance weight is mounted rearward of the plunger and a blade.
The balance weight is formed by two separate portions, namely a base portion and a weight portion disposed in front of the base portion. The weight portion is made relatively heavy so that the position of the overall center of gravity of the balance weight is located more in the front part. This suppresses the rearward or forward moment as shown in FIGS. 10 and 11 of Japanese Patent Application Publication No. 2011-115912 (JP 2011-115912 A).
In the reciprocating saw of Japanese Patent Application Publication No. 2001-347502 (JP 2001-347502 A), the plunger and the saw blade are aligned with the balance weight in the vertical direction, and are not shifted with respect to the balance weight in the longitudinal direction. Accordingly, rearward or forward moment is not generated, and vibration can be easily suppressed.
However, the plunger and the balance weight need to be placed so as to adjoin the gear, and therefore the blade cannot be swung in the longitudinal direction. Accordingly, the blade cannot make orbital motion (longitudinal swinging together with vertical movement), and the cutting force cannot be increased. Moreover, since both the guide member of the plunger and the guide member of the balance weight are received by the single guide groove formed in the single gear, the vertical movement of the plunger is not independent of the vertical movement of the balance weight. Namely, the vertical movement of the plunger and the vertical movement of the balance weight are dependent on each other. Therefore, the vertical movement of the plunger and the vertical movement of the balance weight cannot be adjusted independently.
In the reciprocating tool of Japanese Patent Application Publication No. 2011-115912 (JP 2011-115912 A), the position of the center of gravity of the balance weight is located more in the front part, but the entire balance weight is still shifted with respect to the plunger in the longitudinal direction. As a result, rearward or forward moment is generated, and vibration and noise are generated due to the moment.
Such a balance weight is effective in suppressing vibration of the rod if the weight portion having great mass is disposed on an extended line of the rod. However, when the weight portion moves vertically, the longitudinal moment is generated, which may produce vibration. One solution to this problem is to provide a guide member that guides the vertical movement of the weight portion. However, when the weight portion operates in the longitudinal direction, the guiding function of the guide member is degraded. Accordingly, providing such a guide member is not enough to prevent vibration (Japanese Patent Application Publication No. H11-5201 (JP H11-5201 A)).